This application requests supplemental funds to incorporate human ES cells into research funded by HLBI entitled "Cardiomyocyte Regeneration from Multipotent Precursor Cells" (1 R21 HL71913) that began 10/01/02. A principal goal of the original application was to devise and perform screens for proteins and small molecules that promote efficient differentiation of stem cells, including murine ES cells. Significant species differences between human and animals require that candidate molecules be tested on human cells. Moreover, murine and human ES cells differ considerably in methods of derivation, spontaneous differentiation in culture and range of tissue types that can be formed; thus, it is imperative to incorporate human ES cells wherever possible to avoid missing important leads or following up false positives obtained using animal cells. Specifically, this application requests to incorporate human ES cells to: 1) Perform secondary screens to test if molecules discovered with animal cells also work on human ES cells, and 2) Screen directly for compounds that regulate human ES cell proliferation, potency and cardiomyocyte differentiation. These supplemental aims do not diverge from the originally approved aims; rather, they add human ES cell capability to the existing murine ES program and are essential to bring results closer to clinical application. Towards acquiring ES technology, the laboratory has already: 1) hired a senior investigator experienced in hES culture and HIV lentiviral transduction and cardiomyocyte differentiation of hES cells, 2) negotiated with Geron for technology and the H7 line (NIH code WA07), and 3) purchased and begun culture of lines H1 and H9 (NIH codes WA01,9) from Wicell. [unreadable] [unreadable]